Stress-velocity relationship for hydro-seismological monitoring

Recent advances in hydro-seismology demonstrate that seismic velocity variations provide a sensitive probe of near-surface hydrological processes. Building on earlier physics-based formulations for stress-induced seismic velocity changes, we present a reasonable approximation that recasts these relationships in terms of the ratio μ′/μ, where μ is the shear modulus and μ′ its pressure derivative. This formulation highlights that explicit knowledge of μ′ is not required to obtain physically meaningful predictions of stress-driven seismic velocity variations. Instead, by combining basic geomechanical assumptions with plausible subsurface models for v_p, v_s, and density, μ′/μ can be approximated sufficiently well to enable robust forward modelling.

We show that this approximation unifies previous empirical observations of groundwater-related velocity changes by linking pore-pressure perturbations directly to effective-stress variations and their impact on elastic moduli. The updated framework allows hydro-seismological analyses to be performed in settings where detailed rock-physics constraints are unavailable, broadening its applicability from well-instrumented regions to sparse networks and shallow environmental studies.

This physics-based approach strengthens the foundation for using ambient noise monitoring, coda-wave interferometry, and surface-wave dispersion to track groundwater dynamics and (effective) stress transients. By reducing the dependency on poorly constrained elastic derivatives, the method supports more transferable hydro-seismological monitoring strategies and provides a pathway for integrating seismic observations with hydrological models.